1. Field of the Invention
The present invention is directed to lens systems used for flashlights, bicycle or small vehicle lights, hiking lights, search and rescue lights, medical illumination devices, military lighting devices, and other commercial and industrial applications wherein light from a light source is projected through a lens in order to alter characteristics of the projected beam. More particularly, the present invention is directed to an optical lens system which is particularly adapted for use with a high powered light emitting diode (LED) light source having a hemispherical lens associated therewith. The LED source is designed to be cooperatively seated within a cavity in a rear portion of a projecting lens. The projecting lens includes arcuate side walls which are designed to be totally internally reflective to project light through a front face of the lens from the optically aligned LED source such that substantially all light from the LED source passes through the lens body and through the front face of the lens in a lambertion pattern. Preferably, the projected light beam creates a generally central hot spot by directing the light rays at angles between approximately 5xc2x0 and 30xc2x0 with respect to a central optical axis of the projecting lens.
The present invention is also directed to lenses which are specifically designed to positively optically aligned and secured when mounted within a lens holder whereby heat dissipation from the LED source is assured so as to maintain LED operating temperatures within critically defined operating ranges.
2. Brief Description of the Related Art
It has been know to use various types of solid lenses to direct light emitted from light sources such that light rays are intensified or altered as they pass through the lenses and are projected forwardly of the lenses. Lens configurations are varied to change the projected light pattern to create different lighting characteristics or different fields of projection.
By way of example, in U.S. Pat. No. 2,469,080 to Rosin et al., a unitary lens is disclosed having a projection face and a rear wall having a central cavity extending therein for purposes of providing a chamber for seating a light source. Light from the source is projected laterally and forwardly through the lens and the lateral light is projected or reflected off the inner surfaces of the lens and through the front face of the lens in a collimated pattern wherein the light rays are substantially parallel to one another. With such a lens, the size of the light beam remains generally constant and is generally uniform in intensity across the full width of the beam such that a spot reflected off a surface close to the lens will appear to have approximately the same size as one reflected off a surface which is much farther from the lens.
In U.S. Pat. No. 2,908,197 to Wells et al., a lens for creating a wide angle distribution of light received from a light source is disclosed. In the lens system described, the front face of the lens is altered to create a different light projection pattern. The lens includes a rear cavity in which a light source is seated such that light is projected forwardly and laterally within the lens with the lateral light being reflected from the side walls of the lens forwardly through the various portions of the front face described and shown in the patent. In this manner, different wide angle light patterns are obtained from the light source.
In many instances, lenses are specifically designed for different types of light sources. By way of example, in U.S. Pat. No. 5,757,557 to Medvedev et al., a beam forming lens is disclosed particularly for use with an incandescent light source such as a conventional incandescent bulb. As with other prior art lenses, the lens body includes a front face, tapering side walls and a rear cavity. The cavity is of a size within which the incandescent light source is cooperatively received. Light from the light source is projected substantially 360xc2x0 with respect to the incandescent bulb and is reflected by the inner side walls of the lens forwardly through the front face. As taught in the patent, it is desired that the lens reflect as much energy from the incandescent light source as is possible so that light normally projected rearwardly of the incandescent bulb is projected forwardly in a collimated or parallel beam or pattern from the front face of the lens.
In U.S. Pat. No. 6,547,423 to Marshall et al., an LED optical device is disclosed which is particularly designed to use with light emitting diode (LED) modules for purposes of improving the efficiency and performance of the light being projected from the LED source. The lenses disclosed include both generally planar and shaped outer front faces with each lens including tapered side walls. Each lens further includes a cavity which defines a refractive inner side wall and a refractive end wall or lens in which the LED source is seated. Light from the LED source is projected both forwardly and laterally and the lateral light energy is reflected from the inner reflective walls of the lens such that light projected from the front face of the lens is collimated. In some embodiments, the angle of the light may be modified, however, light rays from the lens remain generally parallel.
Other prior references of interest include U.S. Pat. No. 2,215,900 to Bitner et al., U.S. Pat. No. 2,254,961 to Harris, U.S. Pat. No. 5,813,743 to Maka, U.S. Pat. No. 5,485,317 to Perissinotto et al., U.S. Pat. No. 6,527,419 to Galli and U.S. Pat. No. 6,560,038 to Parkyn, Jr. et al.
From the foregoing, the configuration and elements of a lens system for collecting and projecting light from a source is dependent on features of the source. Thus, lenses that may work well with incandescent light sources will not function for other types of lights such as LED light sources due to different focal as well as other physical characteristics of the differing light sources.
New higher power light emitting diodes are being developed. Examples of such newer high powered LEDs are described in U.S. Pat. No. 6,274,924 to Carey et al., the contents of which are incorporated herein in its entirety by reference. Commercially, high powered LEDs are marketed under the names LUXEON I Emitter, LUXEON III Emitter, LUXEON Star and LUXEON V Star.
The new configuration or physical package of the high power LEDs differs from conventional LEDs and also creates additional problems due to the significant amount of heat developed by the high power LEDs.
The thermal requirements for the new high power LEDs is critical. A junction temperature for such high powered LEDs cannot exceed approximately 120xc2x0 Celsius. High power LEDs can shift to slightly higher wave lengths with a rise in the junction temperature. The human eye is sensitive to color shift and this must also be accounted for in a design of a projection system.
Further, high power LEDs experience a loss of light output as their junction temperature increases. Therefore, the lower the junction temperature maintained, the better the luminous efficiency of the light source. By way of example, if there is exactly enough heat dissipation at an ambient temperature of 10xc2x0 Celsius with respect to the junction temperature, as the temperature rises, the light from the LED will begin to dim.
High power LEDs also become more unreliable when the junction temperatures exceed the maximum designed. The maximum junction temperatures are based upon the allowable thermal stress of encapsulates which surround components of the LEDs, such as silicone. Further, LEDs may have a reduced life expectancy due to temperatures exceeding maximum design temperatures. Newer high power LEDs may have a life expectancy of 100,000 hours while still maintaining 70% of their original efficiencies. However, if temperatures rise above the maximum junction temperature, the high power LEDs will drop to 70% of their original efficiency immediately without regard to number of hours of operation.
Due to the need to maintain temperatures within design limits, new high power LEDs must be utilized with heat sinks to draw heat away from the LED components. If a heat sink is disengaged for only a period of a few minutes, an LED may become permanently damaged or destroyed.
In view of the foregoing, there is a need to design a new lens system for use with high power LED light sources wherein lenses associated with the system not only provide for a maximum reflectance of light energy received from the LED sources but also wherein the lenses are designed to be cooperatively used with holders so as to insure an integrity of heat sinks for maintaining safe operating temperatures of the LEDs during use.
The present invention is directed to a lens system for use with new high power LED light source packages and is specifically designed to project a non-collimated beam of light energy. More particularly, the invention is directed to creating a lambertion projection of light that is free of light distortions and wherein in the overall beam angle is between 5xc2x0 and 30xc2x0 degrees.
The lens system incorporates a solid lens body having a front projecting face which is surrounded by an annular non-optical lip for purposes of providing stability when the lens is mounted within an optical holder. The body of the lens includes a conically tapering sidewall which extends from the front face convexly rearwardly to a rear face such that the side wall is symmetrical with respect to an optical center line or central axis of the lens body extending from the rear face to the front face of the lens. A cavity is formed in the rear face of the lens of a size to cooperatively receive a hemispherical dome or lens cover associated with a high power LED source. The cavity is defined by a cylindrical refractive side wall which is axially aligned with the central axis of the lens and an inner refractive lens wall which may be either planar or convex. To assure proper alignment of the LED source with the projecting lens, a counterbore is provided in the rear face of the lens in which the LED body is mounted. Such mounting will insure the LED cover which seats in the cavity of the projecting lens is perfectly aligned with the optical axis of the lens when the LED is mounted thereto.
Light from the LED passes from the cavity into the body of the lens and is reflected from the inner sidewall of the lens so as to be non-collimating as it passes forwardly of the lens. In preferred embodiments, the lens configuration defines a central hot spot of greater light intensity. Further, light is projected in a lambertion pattern with the overall beam angle being between 5xc2x0 and 30xc2x0 relative to the central axis of the lens.
To provide an accurate alignment of the lens relative to a lens or optic holder, the present invention also provides at least one guide flange which is integrally formed with the lens and which preferably extends radially outward adjacent the rim or lip surrounding the front face of the lens. In some embodiments, a plurality of such guide flanges may be used to appropriately align the lens within a lens holder.
The lens holder of the present invention is designed to insure proper heat dissipation from the LED source such that premature destruction and loss of longevity of the LED light source is effectively prevented.
The lens holder includes a somewhat cylindrical shell which is open at its forward end and substantially closed at its rear or opposite end. Mounted within the holder are one or a plurality of spaced rails which define channels for cooperatively receiving the guide flange or flanges associated with the lens body. In this manner, when the lens is inserted within the holder, the guide flange or flanges will insure accurate placement and retention of the lens within the holder and will also insure that the lens is properly seated with respect to a hemispherical cover of the high powered LED source which is mounted within the optic holder.
The LED source is mounted to heat sink members carried by the holder. One heat sink member includes a base from which a plurality of spaced finger elements extend along the inner surface of the lens holder surrounding the lens. A second heat sink member is mounted in contact with the first heat sink member but is housed in a pocket within the lens holder. The first and second heat sink members are formed of metal and are adhesively connected to conduct heat from the LED source. A metallic heat dissipating tap, such as a screw, engages the second heat sink member and extends therefrom through the body of the lens holder to thereby dissipate heat from the holder. The heat sinks and tap member will effectively dissipate heat from the LED source to maintain operating temperatures of the high powered LED within specific ranges.
As described, to maintain the LED in contact with respect to the heat sinks, the LED is secured to one of the heat sinks by a special high temperature adhesive. Due to the nature of the adhesive, it is critical that no force be placed laterally to create a shearing moment between the LED light source and the heat sinks or premature failure of the LED may occur due to heat buildup caused by an inefficient contact between the LED source and the heat sinks during operation of a lighting unit incorporating the lens system. The relationship between the lens guide flanges and the guide channels of the lens holder prevent such a shearing force.
The optical holder further includes an electrical circuit board for providing power to the LED source and an on/off switch mechanism for supplying power to the circuit board from a conductor connected to a source of power such as a battery. The optical holder is designed to be further enclosed within an outer housing depending upon the ultimate end use of the optical system.
The annular rim or lip which surrounds the front face of the lens body is specifically designed to insure that the lens is properly optically aligned relative to the LED source when placed within the optic holder. The rim or lip is designed to be compression fitted within the optic holder by an outer fitting which is sealed against the annular rim by way of a gasket, O-ring or similar element.
It is the primary object of the present invention to provide a lens system which may be utilized to project light from a high power LED source wherein the lens system is designed to project a non-collimated beam of energy in a lambertion pattern at an angle of 5xc2x0 and 30xc2x0 degrees with respect to a primary axis of the lens body and wherein a hot or intense area of light is developed generally centrally of the projected light beam whereby the appearance of the beam will vary depending on a distance from which the beam is viewed relative to the front face of the projection lens.
It is another object of the present invention to provide a lens system for projecting light from a high power LED light source wherein the lens is structured to provide both an alignment flange as well as a mounting rim or lip to insure proper alignment of the lens with an LED light source carried within a lens holder such that the lens is mounted within the holder without effecting the optical properties of the surfaces of the lens and wherein the LED light source is seated within a cavity and counterbore within the rear of the lens and retained therein without any shearing action being created between the lens and the LED which would tend to interrupt an effective contact between the LED and heat sinks provided within the lens holder.
It is also an object of the present invention to provide a lens for use with high power LEDs wherein the lens and the LED source are mounted within a holder which is provided with effective heat sinks to maintain the temperature of the high power LED within specified operating temperatures thereby maximizing the life span and the efficiency of the LED light source.